Sulfuric acid

Raw materials

1. Sulfur

2. Oxygen

3. Water

Process

a. Contact Process (DCDA)

1. Sulfur burned to produce sulfur dioxide.

S (s) + O₂ (g) → SO₂ (g)

2. The sulfur dioxide is oxidized to sulfur trioxide using oxygen in the presence of vanadium(V)oxide catalyst.

2 SO₂ (g) + O₂ (g) → 2 SO₃ (g) (in presence of V₂O₅)

3. Sulfur trioxide is absorbed into 97–98% H₂SO₄ to form oleum (H₂S₂O₇), also known as fuming sulfuric acid. The oleum is then diluted with water to form concentrated sulfuric acid.

H₂SO₄ (l) + SO₃ → H₂S₂O₇ (l)

H₂S₂O₇ (l) + H₂O (l) → 2 H₂SO₄ (l)

(Note that directly dissolving SO₃ in water, SO₃ (g) + H₂O (l) → H₂SO₄ (l), is not practical due to the highly exothermic nature of the reaction between sulfur trioxide and water. The reaction forms a corrosive aerosol that is very difficult to separate, instead of a liquid.)

b. Wet sulfuric acid process (WSA)

1. Sulfur burned to produce sulfur dioxide.

S(s) + O₂(g) → SO₂(g)

or, alternatively, hydrogen sulfide (H₂S) gas is incinerated to SO₂ gas.

2 H₂S + 3 O₂ → 2 H₂O + 2 SO₂ (−518 kJ/mol)

2. The sulfur dioxide is oxidized to sulfur trioxide using oxygen with vanadium(V)oxide catalyst.

2 SO₂ + O₂ → 2 SO₃ (−99 kJ/mol) (reaction is reversible)

3. The sulfur trioxide is hydrated into sulfuric acid H₂SO₄.

SO₃ + H₂O → H₂SO₄(g) (−101 kJ/mol)

4. The sulfuric acid is condensed to liquid 97–98% H₂SO₄.

H₂SO₄(g) → H₂SO₄(l) (−69 kJ/mol)

Product

Sulfuric acid

Used in

Lead-acid batteries (for cars and other vehicles), ore processing, fertilizer manufacturing, oil refining, wastewater processing, chemical synthesis

Production facility

Port Augusta, SA

Export

Sucre, Bolivia